An API? That's a sad joke. (I say that bitterly as someone who's been knee-deep in the HTML structure of HN for the past few days, trying to parse out data for my own app.)

I talked to someone in #startups a little while ago who was developing a server-side API for HN, but last I heard it wasn't done.

There's a few sites that are sort of "HN aggregators." Unfortunately I've lost the links, but there was one that used a simple algorithm to accumulate the top stories of HN. It would scan the front page every N minutes and give each story X points based on its ranking at the time. Does anyone remember that one?

At any rate, the best you could get from those sites would be a friendlier HTML structure that doesn't feel like 1994. You'll probably have to parse some HTML yourself.